Preparation Of Metal-organic-frameworks Derived Nanomaterials And Their Applications In Supercapacitors

Metal-organic frameworks(MOFs)have been widely used in electrochemical catalysis,lithium-ion batteries,fuel cells,and sodium-ion batteries because of their metal sites and organic linkers.At meanwhile,due to high specific surface area and low density characteristics,MOFs and their derivatives are considered to be the best candidate electrode materials for next-generation secondary-lithium-ion batteries and supercapacitors.currently,increasing researches are focusing on the development of high energy density batteries and high power density supercapacitor electrode materials with MOFs derivatives.The focus of this thesis is to fabricate two novel bimetallic supercapacitor electrode materials with special hollow structure arrays,ultra-high specific capacitance and energy density.Firstly,Cobalt based metal-organic frameworks(Co-MOF)derived cobalt metavanadate-cobalt hydroxide(Co(VO3)2-Co(OH)2)composite electrode with hierarchical and hollow leaf arrays structure was in-situ fabricated on a carbon cloth for supercapacitors positive electrode.After that,we used poplar wood sawdust as a raw material to prepare poplar activated carbon as a negative supercapacitors electrode by high-temperature pyrolyzed and alkali activation.Then,they were assembled as asymmetrical.In the second part,supercapacitors.cobalt-containing metal-organic frameworks(Co-MOF)were used as precursors to fabricate cobalt tetrathiomolybdate(CoMoS4)on nickel foam with nanobar and hollow micro-triangle arrays structures for ultra-high specific capacitance and energy density supercapacitor electrodes The specific research content and main results are as follows:(1)Co-MOF with micro-leaf-like arrays structure was deposited on the surface of the carbon cloth by chemical deposition.Next,we fabricated the Co(VO3)2-Co(OH)2 composite electrode materials by room-temperature substitution reaction.After that,the cyclic voltammetry(CV),galvanostatic charge-discharge(GCD),and electrochemical impedance spectroscopy(EIS)measurements were employed to evaluate their electrochemical performance.Then,the influence of substitution time on morphology and electrochemical performance was discussed.Finally,the reaction mechanism was also analyzed.The results show that the highest area specific capacitance and energy density of the Co(VO3)2-Co(OH)2 composite electrode can reach to 522 mF cm-2 and 0.01795 mWh cm-2,respectively.In addition,the composite electrode possesses ultra-high electrochemical stability(more than 90%of the initial capacitance after 15,000 charge-discharge cycles at a current density of 10 mA cm-2).Subsequently,we used poplar sawdust to pyrolyzed under N2 atmosphere at high temperatures.After the poplar carbon was alkali activated at 900?,a large number of microporous structures with a high specific surface area(701.3 m2 g-1 and average pore size of 3.064 nm)Polar wood-Derived Activated Carbon(PWAC)were prepared.And,through electrochemical measurements,we found that the highest specific capacitance and energy density of poplar activated carbon prepared were 360 F g-1 and 49.45 Wh kg-1.Lastly,we used the as-prepared Co(VO3)2-Co(OH)2 composite electrode as the positive electrode,PWAC as the negative electrode to assembled a quasi-asymmetric supercapacitor,and examine its electrochemical properties.It was noticed that the electrochemical window of as-assembled quasi-asymmetrical supercapacitor can be extended to 0-1.6V and the energy density is 0.0941 mWh cm-2.Compared with the reported literature,the performance is at a higher level.(2)Co-MOF with micro-triangle stucture was first deposited on a nickel foam surface by chemical deposition.After that,a CoMoS4 triangle arrays electrode was fabricated by a hydrothermal reaction to Co-MOF precursor.Afterwards,we measured the electrochemical properties of the as-prepared bimetallic-sulfide-electrode.At the same time,the influence of the hydrothermal temperature of the fabricated CoMoS4 electrode on the electrochemical performance and surface morphology was also discussed.Electrochemical measurement results show that the maximum specific capacitance and energy density of as-prepared CoMoS4 electrode was 1800 F g-1 and 40.01 Wh kg-1,respectively.These values are significantly higher than previous reported CoMoS4 supercapacitor electrode materials.